Membrane comprising oxyethylene groups

ABSTRACT

The present invention relates to a membrane wherein said membrane comprises a polymerized composition that comprised prior to polymerization at least one type of compound comprising at least 70 oxyethylene groups and at least two polymerizable groups. The invention further relates to the use of this membrane for separating polar gases and vapors.

This application is a 371 filing based on PCT/NL2008/050311 filed May26, 2008 and claiming priority from European Application No. 07108820.7,filed May 24, 2007.

FIELD OF THE INVENTION

This invention relates to membranes that may be obtained by polymerizingcompounds comprising oxyethylene groups. The membranes are particularlyuseful for performing gas separation. The invention also relates toprocesses for preparing said membranes, as well as to their use.

BACKGROUND OF THE INVENTION

For purifying gaseous mixtures e.g. natural gas and flue gas, separatingundesired components from the main stream can in some cases be achievedbased on the relative size of the components (size-sieving). Sometimesbetter results can be achieved by making use of the properties of thecomponents to be separated. For example, U.S. Pat. No. 4,963,165describes the separation of polar from non-polar components usingmembranes made from polyamide-polyether block copolymers which do notappear to be crosslinked. Polyethylene oxide (PEO) based membranes havebeen described as suitable for separating CO₂ from hydrogen and methane(Lin et al., Macromolecules, Vol. 38, no. 20, 2005, 8394-8407).JP8024602A and JP8024603A describe gas separation membranes containing apolyalkylene glycol di(meth)acrylate having 1-24 alkylene glycolrepeating units. Hirayama et al, Journal of Membrane Science, 160,(1999), 87-99, describe polymer films made from polyethylene glycolmono- and di-methacrylates and their application for gas separation.JP7060079 describes plasma treated films having a hydrophilic surfacecomprising oxyethylene groups preferably having 2-30 repeating units.U.S. Pat. No. 5,069,926 describes porous ultrafiltration membranessuitable for the separation of oil and water which have been surfacemodified with plasma- or ozone-treated polyethylene glycol diacrylates.WO-A-2005/097304 describes membrane stacks comprising macroporousgel-filled membranes wherein polyethylene glycol diacrylates are used ascross-linkers.

There is a need for membranes having high permeability and selectivityfor desired gases that are strong and flexible. Ideally such membranescan be produced efficiently at high speeds using toxicologicallyacceptable liquids (particularly water) in the composition. In thismanner the membranes of the present invention can be made in aparticularly cost effective manner. This invention aims at achievingthese targets, at least in part.

SUMMARY OF THE INVENTION

It is thus an object of the present invention to provide a membranehaving good permeation characteristics, in particular for polar gasesand vapors, and that can be produced in an efficient manner. It isanother object to provide a membrane that is strong and robust that doesnot crack easily upon handling.

It has been found that these objects can be met by a membrane made bypolymerizing a composition comprising a compound comprising at least 70oxyethylene —(—CH₂—CH₂—O—)— groups and at least two polymerizablegroups. Thus, in one aspect, the present invention is directed to amembrane comprising the polymerization product of a compound, whichcompound comprises at least 70 oxyethylene groups and at least twopolymerizable groups. For convenience the compound comprising at least70 oxyethylene groups and at least two polymerizable groups is oftenreferred to in this description as “the crosslinkable monomer”.

DETAILED DESCRIPTION

It is an object of this invention to provide a membrane that has a highpermeability to polar gases such as CO₂, H₂S, NH₃, SO₄, and nitrogenoxides, especially NO_(x) and a high selectivity for these polar gasesover non-polar gases, vapors and liquids. The gases may comprise vapors,for example water vapor. In one embodiment the membrane is not permeableto liquids, e.g. water and aqueous solutions.

Such a gas separation membrane can be applied for purifying natural gas(a mixture which predominantly comprises methane) by removing polargases (CO₂, H₂S), for removing CO₂ from hydrogen and from flue gases.Flue gas is typically gas that exits to the atmosphere via a flue, whichis e.g. a pipe or channel for conveying exhaust gases from a fireplace,oven, furnace, combustion engine, boiler or steam generator.Particularly, it refers to the combustion exhaust gas produced at powerplants. Its composition depends on what is being burned, but it willusually consist of mostly nitrogen (typically more than two-thirds)derived from the combustion air, carbon dioxide (CO₂) and water vapor aswell as excess oxygen (also derived from the combustion air). It furthercontains a small percentage of pollutants such as particulate matter,carbon monoxide, nitrogen oxides and sulfur oxides. Recently theseparation and capture of CO₂ has attracted attention in relation toenvironmental issues (global warming). For some customers and in someapplications the cost of the membranes are an important consideration.

The membrane of the invention is made by polymerization compoundscomprising at least 70 oxyethylene groups. While not wishing to belimited by any particular theory, we believe the numerous oxyethylenegroups interact with polar molecules such as CO₂ very differently thanwith non-polar molecules such as N₂, which makes membranes based onpolymers of these compounds suitable for enhancing selectivity for polarover non-polar molecules. An oxyethylene group may be drawn out in fullas —(—CH₂—CH₂—O—)—.

A higher number of oxyethylene groups improves the permeability to polargases. Surprisingly not only permeability and selectivity improve with ahigh number of oxyethylene groups but also the physical strength of theresulting membrane is significantly better. Membranes made frompolymerizable compounds having a low number of oxyethylene groups appearto be brittle and break easily when bended during handling. This isespecially important when the membrane is used without support. But alsoattached to a porous support a flexible structure is desired to reducethe risk of cracking of the membrane.

Preferably the polymerization is performed by a process comprisingapplication of the composition to a substrate, e.g. to form a thin layerthereon, and polymerizing the crosslinkable monomer(s) to provide themembrane in the form of a polymer film on the substrate. In this way amembrane may be produced at low cost and at a high production rate (highapplication/coating speeds). In one embodiment the substrate is anon-porous substrate. In this embodiment the resultant membranepreferably is removed from the substrate after polymerization. Inanother embodiment the substrate is porous and the resultant membraneand porous substrate preferably remain in contact. The latteralternative can be very useful for providing membranes with greatermechanical strength and the process for making such supported membranesis particularly efficient and convenient.

Optionally the process further comprises the step of washing and/ordrying the membrane after polymerization.

Lin et al. (Macromolecules 38 (2005) 8381-8407, 9679-9687) describe PEGcontaining polymers with polymerizable groups vinyl groups, whichpolymers have 14 oxyethylene segments. Similar polymers are described inLin et al. (Journal of Membrane Science 276 (2006) 145-161); Lin et al.(Macromolecules 39 (2006) 3568-3580; and Lin et al. (Advanced Materials18 (2006) 39-44). Although in these publications studies are reported onthe permeability properties of membranes produced from these polymers,there is no disclosure or suggestion that the physical strength can beimproved considerably by preparing a membrane comprising a polymerhaving the specific chemical composition of the present invention. Inparticular, these prior art documents are silent with respect to thenumber of oxyethylene groups and polymerizable groups on the membrane'sphysical characteristics.

For a membrane to be effective as separation membrane the size of thepores should in general be smaller than the dimensions of the compoundsto be separated. For separation of small gaseous molecules the membraneis substantially non-porous which means that its pore sizes preferablydo not exceed the radius of the molecule to be rejected. A suitablemethod to determine the pore size is observation by scanning electronmicroscope (SEM). Substantially non-porous means that no pores aredetected by SEM (using a Jeol JSM-6335F Field Emission SEM, applying anaccelerating voltage of 2 kV, working distance 4 mm, aperture 4, samplecoated with Pt with a thickness of 1.5 nm, magnification 100 000×, 3°tilted view). Preferably the membrane has an average pore size of below10 nm, more preferably below 5 nm, especially below 2 nm. The maximumpreferred pore size depends on the application e.g. on the compounds tobe separated. Another method to obtain an indication of the actualporosity is the permeance to liquids such as water. Preferably thepermeance to liquids is very low, i.e. the average pore size of themembrane is such that the pure water permeance at 20° C. is less than6.10⁻⁸ m³/m²·s·kPa, more preferably less than 3.10⁻⁸ m³/m²·s·kPa.

The composition optionally comprises one of the crosslinkable monomersor it may contain more than one of the crosslinkable monomers,optionally other compounds that may copolymerize therewith. These othercompounds include higher oxyalkylenes, such as oxypropylenes andoxybutylenes, and may be present in the composition although low amountsof such polymerizable higher oxyalkylenes are preferred (e.g 0 to 10weight % relative to the polymerizable composition) because of theirless hydrophilic character, their higher price and their more limitedcommercial availability.

For the final membrane linear polymers containing oxyethylene groups arenot suited as such since they may partly or totally dissolve in contactwith liquids or vapors causing permanent damage to the membrane. Toreduce the tendency to dissolve in contact with liquids or vapors it wasfound that a crosslinked structure is required. For making a networkstructure at least two crosslinkable groups per molecule should bepresent. Examples of suitable crosslinkable groups are acrylate groups,methacrylate groups, acrylamide groups, vinyl ether groups, vinyl estergroups, vinyl amide groups, allyl ether groups, allyl ester groups,allyl amine groups, allyl amide groups, styryl groups, maleic groups,fumaric groups, glutaconic groups, itaconic groups, citraconic groups,mesaconic groups, tiglic groups, angelic groups, senecioic groups andcombinations thereof. The preferred crosslinkable groups are acrylic(CH₂═CHC(O)—) groups, especially acrylate (CH₂═CHC(O)O—) groups.Acrylate groups are preferred because of their fast polymerizationrates, especially when using UV light to effect the polymerization, andbetter commercial availability.

Preferably the ethylenically unsaturated group in the crosslinkablegroup is not substituted. Polymers of substituted ethylenicallyunsaturated monomers have a lower oxyethylene content than polymers ofnon-substituted ethylenically unsaturated monomers, resulting in a lowerpermeability and possibly lower selectivity for polar gases/vapors. Itis known that in general substituted ethylenically unsaturated monomersare less reactive than non-substituted ethylenically unsaturatedmonomers due to steric hindrance, which will result in slowerpolymerization. For high speed production methods fast polymerization isdesired. In case substituted ethylenically unsaturated groups are used ahigh energy polymerization method is preferred such as electron beamirradiation of plasma treatment. Even with these methods unsubstitutedethylenically unsaturated monomers are preferred.

The network structure is determined to a large extent by the content ofmultifunctional monomers having two or more crosslinkable groups and bythe distance between these crosslinkable groups. A high content of di-,tri- or tetra-functional monomers will result is a rigid structure. Fora good performance a rigid structure is generally not desired: thepermeability is restricted. A more loose matrix can be achieved bylimiting the content of multifunctional monomers and increasing thecontent of monofunctional monomers. Monofunctional monomers arepolymerizable and will be incorporated in the network structure butcannot form crosslinks. A low content of multifunctional monomers (e.g.less than 3 weight %) will result in a loose structure which is notpreferred because it has a negative effect on the selectivity. Also theefficiency of the crosslinking reaction decreases, making a longerreaction time necessary with more strict reaction conditions e.g.reaction under an inert atmosphere. A more preferred method to achieve alow crosslink density is to increase the distance between thecrosslinkable groups by applying high molar weight (MW) monomers,wherein in the case of difunctional monomers the crosslinkable groupsare preferably located on the ends of the (linear) molecule. Themolecular weight of the crosslinkable monomer is preferably at least3200 Da, more preferably at least 4000 Da. Molecular weights as high as20, 40 or even 60 kDa or more may be used. A practical higher limit isformed by the viscosity of the composition comprising the polymerizablecompound which is preferably less than 4000 mPa·s at 35° C. Preferablythe molecular weight of the polymerizable compound is lower than 100kDa.

The oxyethylene groups in the polymerizable compound may form anuninterrupted chain of such groups (e.g. as in —(CH₂ CH₂O)_(n)— whereinn is at least 70) or the chain may contain interruptions as—(CH₂CH₂O)_(n-q)—R—(OCH₂CH₂)_(q)— (wherein q is 1 to n−1). Examples ofsuch interruptions (R) include —CH₂—, —(CH₂)_(x)— wherein x>2,—CH(CH₃)—, —C(CH₃)₂—, —CH₂—C(CH₃)₂—CH₂—, —C₆H₄—, —C₆H₄—C(CH₃)₂—C₆H₄—(bisphenol A), —(C═O)—. Preferably, at least two vinyl groups areseparated by at least 15, more preferably at least 25 or 35 oxyethylenegroups. A high oxyethylene content is preferred because it enhances thesolubility of carbon dioxide in the matrix due to its hydrophiliccharacter and thereby improves the permeability. Preferably at least 75weight %, more preferably at least 80 weight % of oxyethylene groups arepresent in the crosslinkable monomer. For some embodiments even morethan 90 weight % of oxyethylene groups is preferred. Preferably at most99.85 weight % of the crosslinkable monomer is oxyethylene groups. Thereis no limitation to the maximum number of oxyethylene groups between twocrosslinkable groups, but crystallization of the poly-oxyethylene chainunder the conditions the membrane is used should be prevented as much aspossible, because in crystallized form the flux is severely reduced.Membranes with matrices crystallizing at or below room temperature canbe used without such negative effects on the flux for high temperatureapplications, like separation of flue gas or water vapor, etc. Usingstructures comprising one or more non-oxyethylene groups may beeffective in preventing crystallization. In the final structure othercompounds may be incorporated in the polymer film and therefore theoverall oxyethylene content may be lower than in the crosslinkablemonomer. Preferably oxyethylene groups constitute at least 50 weight %of the polymer film, more preferably at least 60 weight %, even morepreferably up to 70 weight % or 80 weight %. Preferred upper limit forthe content of oxyethylene groups in the membrane is 98 weight % or 95weight %.

In general, a combination of several types of monomers is preferred. Forinstance with a mixture of difunctional crosslinkable monomers andmonofunctional monomers good results can be obtained. Alternativelyhigher functional monomers may be used but usually in low amounts sincehigh amounts would result in a high crosslinking density and a rigidstructure. Preferably the composition comprises between 0 and 10 weight% of higher functional monomers (e.g. having 3 or more crosslinkablegroups), more preferably between 0 and 5 weight %. The composition to bepolymerized preferably comprises between 3 and 80 weight % ofcrosslinkable monomer and may further comprise monofunctional monomers,different kinds of additives and solvents. More preferably thecomposition comprises between 5 and 60 weight %, even more preferablybetween 10 and 50 weight % of crosslinkable monomer. More than one typeof crosslinkable monomer may be used.

Suitable crosslinkable monomers can be described according the followinggeneral formulae:

wherein

-   a is at least 70/m and less than 1100.-   m is 2-6, preferably 2.-   R^(m) is a polyvalent radical corresponding to m: R² (m=2), R³    (m=3), R⁴ (m=4), R⁵ (m=5), R⁶ (m=6).-   p is more than 1 and less than 500, preferably between 1 and 100.-   z is at least 70/p and less than 1100.-   R² is R²¹ or R²², where R²¹ is for example alkylene group    —(CH₂)_(x)—, —C(CH₃)₂—, —CH₂—C(CH₃)₂—CH₂—, —C₆H₄—, —C₆HR¹ ₃—,    —C₆H₂R¹ ₂—, —C₆H₃R¹—, —C₆H₄—CH₂—C₆H₄—, —C₆H₄—CH(CH₃)—C₆H₄—,    —C₆H₄—C(CH₃)₂—C₆H₄—, or polyalkylene glycol (e.g. poly(propylene    glycol, poly(butylene glycol), poly(trimethylene glycol),    poly(tetramethylene glycol)).-   R²² is for example a carbonyl group —C(═O)— or dicarboxylic group of    formula: —C(═O)—R²¹—C(═O)—, dicarbamate group of formula:    —C(═O)—NH—R²¹—NH—C(═O)—, or biscarbonate group of formula:    —C(═O)—O—R²¹—O—C(═O)—.-   wherein x is 1-10 and R¹ is H, or an alkyl group of C₁-C₁₀, or an    aromatic group, or an alkoxy group, or an ester group.-   Examples of R³:

-   Examples of R⁴:

-   Example of R⁶:

-   Y₁— and Y₂— are for example —(C═O)—O—, —C(═O)—O—(CH₂)_(x)—O—,    —C(═O)—NR¹—, —C(═O)—NR¹—(CH₂)_(x)—O—, —C(═O)—OCH₂—CH(OH)—CH₂O—,    —C(═O)—OCH₂—CH(OH)—CH₂NR¹—, —C₆H₄—, CH₂═CH—O—,    —O—C(═O)—(CH₂)_(x)—O—, —S—, —NR¹—, —NH—C(═O)—(CH₂)_(x)—O—, —CH₂—O—,    —CH₂—O—C(═O)—(CH₂)_(x)—O—, —CH₂—NH—C(═O)—(CH₂)_(x)—O—, —SiR¹ ₃—,    —CH₂—SiR¹ ₃—.-   wherein x is 1-10 and R¹ is H, or an alkyl group of C₁-C₁₀, or an    aromatic group, or an alkoxy group, or an ester group.-   Total number of oxyethylene groups in the molecule n=z*m or n=z*p.

Examples of specific compounds include: Poly(ethylene glycol)diacrylate, Poly(ethylene glycol) divinyl ether, Poly(ethylene glycol)diallyl ether, Bisphenol A ethoxylate diacrylate, neopentyl glycolethoxylate diacrylate, propanediol ethoxylate diacrylate, butanediolethoxylate diacrylate, hexanediol ethoxylate diacrylate, poly(ethyleneglycol-co-propylene glycol) diacrylate, Poly(ethyleneglycol)-block-poly(propylene glycol)-block-poly(ethylene glycol)diacrylate, Glycerol ethoxylate triacrylate, trimethylolpropaneethoxylate triacrylate, trimethylolpropane ethoxylate triacrylate,pentaerythrytol ethoxylate tetraacrylate, ditrimethylolpropaneethoxylate tetraacrylate, dipentaerythrytol ethoxylate hexaacrylate.

In general, the preferred composition comprises copolymerization of thepolymerizable compound with one or more other ethylenically unsaturatedcompounds. For instance, copolymerization of the polymerizable compoundwith monofunctional monomers (i.e. compounds having 1 ethylenicallyunsaturated group) can give good results, a higher permeability can beobtained. Preferably these other ethylenically unsaturated compoundsalso comprise a high number of oxyethylene groups, e.g. at least 25oxyethylene groups. Alternatively higher functional monomers may be usedbut usually in low amounts to prevent a too high crosslink density.

Examples of compounds having one (and only one) ethylenicallyunsaturated groups include alkyl (meth)acrylates, (meth)acrylic acid,(meth)acrylamide, (meth)acrylonitrile, vinyl pyridine, vinylpyrrolidone, vinylacetate, and poly(ethylene glycol) (meth)acrylate offollowing structure, wherein w is 1-100 and R¹¹ is H or an alkyl groupof C₁-C₁₀ or an aromatic group or an alkoxy group or an ester group, andR¹² is H or a methyl group.

In general the dry thickness of the membrane of this invention inisolated form may typically be between 20 μm and 300 μm, more preferablybetween 30 and 200 μm. When joined to a support the membrane need notgive internal strength and the optimal thickness is based on propertiessuch as permeability and uniformity. In the latter case the drythickness of the membrane layer is typically between 0.05 and 10 μm,more preferably between 0.05 and 2 μm. The permeance to gases and vaporsis directly related to the thickness of the membrane layer, so a layeras thin as possible is preferred. On the other hand the layer should beuniform without defects such as pinholes that would deteriorate theselectivity.

The crosslinkable monomers comprising at least 70 oxyethylene groups arepreferably well soluble in polar solvents such as water. For reasons ofsafety, health and the environment, as well as from economic viewpoint,water is the most preferred solvent.

Typically the solvent comprises water and optionally one or more organicsolvents, especially water-miscible organic solvent(s). As examples ofwater-miscible organic solvents there may be mentioned: C₁₋₆-alkanols,preferably methanol, ethanol, n-propanol, isopropanol, n-butanol,sec-butanol, tert-butanol, n-pentanol, cyclopentanol and cyclohexanol;linear amides, preferably dimethylformamide or dimethylacetamide;ketones and ketone-alcohols, preferably acetone, methyl ether ketone,cyclohexanone and diacetone alcohol; water-miscible ethers, preferablytetrahydrofuran and dioxane; diols, preferably diols having from 2 to 12carbon atoms, for example pentane-1,5-diol, ethylene glycol, propyleneglycol, butylene glycol, pentylene glycol, hexylene glycol andthiodiglycol and oligo- and poly-alkyleneglycols, preferably diethyleneglycol, triethylene glycol, polyethylene glycol and polypropyleneglycol; triols, preferably glycerol and 1,2,6-hexanetriol;mono-C₁₋₄-alkyl ethers of diols, preferably mono-C₁₋₄-alkyl ethers ofdiols having 2 to 12 carbon atoms, especially 2-methoxyethanol,2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)-ethanol,2-[2-(2-methoxyethoxy)ethoxy]ethanol,2-[2-(2-ethoxyethoxy)-ethoxy]-ethanol and ethyleneglycol monoallylether;cyclic amides, preferably 2-pyrrolidone, N-methyl-2-pyrrolidone,N-ethyl-2-pyrrolidone, caprolactam and 1,3-dimethylimidazolidone; cyclicesters, preferably caprolactone; sulphoxides, preferably dimethylsulphoxide and sulpholane.

In case a solvent is used in the composition, the solvent is chosen sothat a stable and homogeneous solution is formed which does not phaseseparate upon polymerization of the polymerizable compound.

The polymerizable compound mixture is preferably subjected to radiationto effect polymerization. In principle (electromagnetic) radiation ofany suitable wavelength can be used, such as for example ultraviolet,visible or infrared radiation, as long as it matches the absorptionspectrum of the photo-initiator, if present, or as long as enough energyis provided to directly polymerize (or cure) the polymerizable compoundwithout the need of a photo-initiator. Electron beam radiation may alsobe used. The terms curing and polymerization are used interchangeablythroughout this document.

Curing by infrared radiation is also known as thermal curing. Thuspolymerization may be effectuated by combining the monomers withethylenically unsaturated groups with a thermally reactive free radicalinitiator and heating the mixture. Exemplary thermally reactive freeradical initiators are organic peroxides such as ethyl peroxide andbenzyl peroxide; hydroperoxides such as methyl hydroperoxide, acyloinssuch as benzoin; certain azo compounds such asα,α′-azobisisobutyronitrile and γ,γ-azobis(γ-cyanovaleric acid);persulfates; peracetates such as methyl peracetate and tert-butylperacetate; peroxalates such as dimethyl peroxalate and di(tert-butyl)peroxalate; disulfides such as dimethyl thiuram disulfide and ketoneperoxides such as methyl ethyl ketone peroxide. Temperatures in therange of from about 30° C. to about 150° C. are generally employed. Moreoften, temperatures in the range of from about 40° C. to about 110° C.are used.

Of all the abovementioned methods of polymerisation the use ofultraviolet light is preferred. Suitable wavelengths are for instanceUV-A (400-320 nm), UV-B (320-280 nm), UV-C (280-200 nm), provided thewavelength matches with the absorbing wavelength of the photo-initiator,if present.

Suitable sources of ultraviolet light are mercury arc lamps, carbon arclamps, low pressure mercury lamps, medium pressure mercury lamps, highpressure mercury lamps, swirlflow plasma arc lamps, metal halide lamps,xenon lamps, tungsten lamps, halogen lamps, lasers and ultraviolet lightemitting diodes. Particularly preferred are ultraviolet light emittinglamps of the medium or high pressure mercury vapor type. In addition,additives such as metal halides may be present to modify the emissionspectrum of the lamp. In most cases lamps with emission maxima between200 and 450 nm are most suitable.

The energy output of the exposing device may be between 20 and 1000W/cm, preferably between 40 and 500 W/cm but may be higher or lower aslong as the desired exposure dose can be realized. The exposureintensity is one of the parameters that can be used to control theextent of curing which influences the final structure of the membrane.Preferably the exposure dose is at least 40 mJ/cm², more preferablybetween 40 and 600 mJ/cm², most preferably between 70 and 220 mJ/cm² asmeasured by an High Energy UV Radiometer (UV Power Puck™ fromEIT—Instrument Markets) in the UV-B range indicated by the apparatus.Exposure times can be chosen freely but preferably are short and aretypically less than 5 seconds, preferably less than 2 seconds, e.g. lessthan 1 second. For determining exposure time only the direct radiationincluding the radiation reflected by the mirror of the exposure unit istaken into account, not the indirect stray light.

Photo-initiators may be used in accordance with the present inventionand can be mixed into the mixture of the polymerizable compound(s).Photo-initiators are usually required when the coated mixture is curedby UV or visible light radiation. Suitable photo-initiators are thoseknown in the art such as radical type, cation type or anion typephoto-initiators.

Examples of radical type I photo-initiators are α-hydroxyalkylketones,such as 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone(Irgacure™ 2959: Ciba),2-hydroxy-1-[4-(2-hydroxypropoxy)phenyl]-2-methyl-1-propanone (Omnirad™669: Ciba), 1-hydroxy-cyclohexyl-phenylketone (Irgacure™ 184: Ciba),2-hydroxy-2-methyl-1-phenyl-1-propanone (Sarcure™ SR1173: Sartomer,Additol™ HDMAP: Surface Specialties),oligo[2-hydroxy-2-methyl-1-{4-(1-methylvinyl)phenyl}propanone](Sarcure™SR1130: Sartomer),2-hydroxy-2-methyl-1-(4-tert-butyl-)phenylpropan-1-one,2-hydroxy-[4′-(2-hydroxypropoxy)phenyl]-2-methylpropan-1-one,1-(4-Isopropylphenyl)-2-hydroxy-2-methyl-propanone (Darcure™ 1116:Ciba); α-aminoalkylphenones such as2-benzyl-2-(dimethylamino)-4′-morpholinobutyrophenone (Irgacure™ 369:Ciba), 2-methyl-4′-(methylthio)-2-morpholinopropiophenone (Irgacure™907: Ciba); α,α-dialkoxyacetophenones such asα,α-dimethoxy-α-phenylacetophenone (Irgacure™ 651: Ciba),2,2-diethyoxy-1,2-diphenylethanone (Uvatone™ 8302: Upjohn),α,α-diethoxyacetophenone (DEAP: Rahn), α,α-di-(n-butoxy)acetophenone(Uvatone™ 8301; Upjohn); phenylglyoxolates such as methylbenzoylformate(Darocure™ MBF: Ciba); benzoin derivatives such as benzoin (Esacure™ BO:Lamberti), benzoin alkyl ethers (ethyl, isopropyl, n-butyl, iso-butyl,etc.), benzylbenzoin benzyl ethers, Anisoin; mono- and bis-Acylphosphineoxides, such as 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (Lucirin™TPO: BASF), ethyl-2,4,6-trimethylbenzoylphenylphosphinate (Lucirin™TPO-L: BASF), bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide(Irgacure™ 819: Ciba),bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphineoxide(Irgacure™ 1800 or 1870). Other commercially available photo-initiatorsare 1-[4-(phenylthio)-2-(O-benzoyloxime)]-1,2-octanedione (Irgacure™OXE01)1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyloxime)ethanone(Irgacure™ OXE02),2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methyl-propan-1-one(Irgacure™ 127), oxy-phenyl-acetic acid 2-[2oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester (Irgacure™ 754),oxy-phenyl-acetic-2-[2-hydroxy-ethoxy]-ethyl ester (Irgacure™ 754),2-(dimethylamino)-2-(4-methylbenzyl)-1-[4-(4-morpholinyl)phenyl]-1-butanone(Irgacure™ 379),1-[4-[4-benzoylphenyl)thio]phenyl]-2-methyl-2-[(4-methylphenyl)sulfonyl)]-1-propanone(Esacure™ 1001M from Lamberti), 2,2′-bis(2-chlorophenyl)-4,4′,5,5′-tetraphenyl-1,2′-bisimidazole (Omnirad™ BCIM from IGM).

Examples of type II photo-initiators are benzophenone derivatives suchas benzophenone (Additol™ BP: UCB), 4-hydroxybenzophenone,3-hydroxybenzophenone, 4,4′-dihydroxybenzophenone,2,4,6-trimethylbenzophenone, 2-methylbenzophenone, 3-methylbenzophenone,4-methylbenzophenone, 2,5-dimethylbenzophenone,3,4-dimethylbenzophenone, 4-(dimethylamino)benzophenone,[4-(4-methylphenylthio)phenyl]phenylmethanone, 3,3′-dimethyl-4-methoxybenzophenone, methyl-2-benzoylbenzoate, 4-phenylbenzophenone,4,4-bis(dimethylamino)benzophenone, 4,4-bis(diethylamino)benzophenone,4,4-bis(ethylmethylamino)benzophenone,4-benzoyl-N,N,N-trimethylbenzenemethanaminium chloride,2-hydroxy-3-(4-benzoylphenoxy)-N,N,N-trimethyl-1-propanamium chloride,4-(13-Acryloyl-1,4,7,10,13-pentaoxatridecyl)benzophenone (Uvecryl™ P36:UCB),4-benzoyl-N,N-dimethyl-N-[2-(1-oxo-2-propenyl)oy]ethylbenzenemethanaminiumchloride, 4-benzoyl-4′-methyldiphenyl sulphide, anthraquinone,ethylanthraquinone, anthraquinone-2-sulfonic acid sodium salt,dibenzosuberenone; acetophenone derivatives such as acetophenone,4′-phenoxyacetophenone, 4′-hydroxyacetophenone, 3′-hydroxyacetophenone,3′-ethoxyacetophenone; thioxanthenone derivatives such asthioxanthenone, 2-chlorothioxanthenone, 4-chlorothioxanthenone,2-isopropylthioxanthenone, 4-isopropylthioxanthenone,2,4-dimethylthioxanthenone, 2,4-diethylthioxanthenone,2-hydroxy-3-(3,4-dimethyl-9-oxo-9H-thioxanthon-2-yloxy)-N,N,N-trimethyl-1-propanaminiumchloride (Kayacure™ QTX: Nippon Kayaku); diones such as benzyl,camphorquinone, 4,4′-dimethylbenzyl, phenanthrenequinone,phenylpropanedione; dimethylanilines such as4,4′,4″-methylidyne-tris(N,N-dimethylaniline) (Omnirad™ LCV from IGM);imidazole derivatives such as2,2′-bis(2-chlorophenyl)-4,4′,5,5′-tetraphenyl-1,2′-bisimidazole;titanocenes such asbis(eta-5-2,4-cyclopentadiene-1-yl)-bis-[2,6-difluoro-3-1H-pyrrol-1-yl]phenyl]titanium(Irgacure™784: Ciba); iodonium salt such as iodonium,(4-methylphenyl)-[4-(2-methylpropyl-phenyl)-hexafluorophosphate (1-). Ifdesired combinations of photo-initiators may also be used.

For acrylates, diacrylates, triacrylates or multifunctional acrylates,type I photo-initiators are preferred. Especiallyalpha-hydroxyalkylphenones, such as 2-hydroxy-2-methyl-1-phenylpropan-1-one, 2-hydroxy-2-methyl-1-(4-tert-butyl-) phenylpropan-1-one,2-hydroxy-[4′-(2-hydroxypropoxy)phenyl]-2-methylpropan-1-one,2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl propan-1-one,1-hydroxycyclohexylphenylketone andoligo[2-hydroxy-2-methyl-1-{4-(1-methylvinyl)phenyl}propanone],alpha-aminoalkylphenones, alpha-sulfonylalkylphenones and acylphosphineoxides such as 2,4,6-trimethylbenzoyl-diphenylphosphine oxide,ethyl-2,4,6-trimethylbenzoyl-phenylphosphinate andbis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, are preferred.Preferably the ratio of photo-initiator and polymerizable compound(s) isbetween 0.001 and 0.1, more preferably between 0.005 and 0.05, based onweight. It is preferred to minimize the amount of photo-initiator used,in other words preferably all photo-initiator has reacted after thecuring step (or curing steps). Remaining photo-initiator may haveadverse effects and when applied as a separation membrane excessivewashing may be required to wash out remaining photo-initiator. A singletype of photo-initiator may be used but also a combination of severaldifferent types.

In the case UV radiation is used a UV light source can be selectedhaving emissions at several wavelengths. The combination of UV lightsource and photo-initiator(s) can be optimized so that sufficientradiation penetrates deep into the layer(s) to activate thephoto-initiators. A typical example is an H-bulb with an output of 600Watts/inch (240 W/cm) as supplied by Fusion UV Systems which hasemission maxima around 220 nm, 255 nm, 300 nm, 310 nm, 365 nm, 405 nm,435 nm, 550 nm and 580 nm. Alternatives are the V-bulb and the D-bulbwhich have a different emission spectrum, with main emissions between350 and 450 nm and above 400 nm respectively. Preferably the UV lightsource and the photo-initiators are chosen such that the wavelength ofthe UV light provided corresponds to the absorption of the photoinitiator(s). From a choice of light sources and photo-initiatorsoptimal combinations can be made. Applying multiple types ofphoto-initiator allows for thicker layers to be cured efficiently withthe same intensity of irradiation.

In case no photo-initiator is added, the polymerizable compound can beadvantageously cured by electron-beam exposure as is known in the art.Preferably the output is between 50 and 300 keV. Curing can also beachieved by plasma or corona exposure.

Curing rates may be increased by adding amine synergists to thepolymerizable compound. Amine synergists are known to enhance reactivityand retard oxygen inhibition. Suitable amine synergists are e.g. freealkyl amines such as triethylamine, methyldiethanol amine, triethanolamine; aromatic amine such as 2-ethylhexyl-4-dimethylaminobenzoate,ethyl-4-dimethylaminobenzoate and also polymeric amines aspolyallylamine and its derivatives. Curable amine synergists such asethylenically unsaturated amines (e.g. (meth)acrylated amines) arepreferable since their use will give less odor due to its ability to beincorporated into the polymeric matrix by curing. The amount of aminesynergists is preferably from 0.1-10 wt. % based on the weight ofpolymerizable compounds in the polymerizable composition, morepreferably from 0.3-3 wt. % based on the weight of polymerizablecompounds.

Where desired, a surfactant or combination of surfactants may be addedto the polymerizable composition as a wetting agent or to adjust surfacetension. Commercially available surfactants may be utilized, includingradiation-curable surfactants. Surfactants suitable for use in thepolymerizable composition include nonionic surfactants, ionicsurfactants, amphoteric surfactants and combinations thereof. Preferrednonionic surfactants include ethoxylated alkylphenols, ethoxylated fattyalcohols, ethylene oxide/propylene oxide block copolymers, fluoroalkylethers, and the like. Preferred ionic surfactants include, but are notlimited to, the following: alkyltrimethylammonium salts wherein thealkyl group typically contains from 8 to 22 (preferably 12 to 18) carbonatoms; alkylbenzyldimethylammonium salts wherein the alkyl grouptypically contains from 8 to 22 (preferably 12 to 18) carbon atoms, andethylsulfate; and alkylpyridinium salts wherein the alkyl grouptypically contains from 8 to 22 (preferably 12 to 18) carbon atoms.Surfactants may be for instance fluorine based or silicon based.Examples of suitable fluorosurfactants are: fluoro alkylcarboxylic acidsand salts thereof, disodium N-perfluorooctanesulfonyl glutamate, sodium3-(fluoro-C₆-C₁₁ alkyloxy)-1-C₃-C₄ alkyl sulfonates, sodium3-(omega-fluoro-C₆-C₈ alkanoyl-N-ethylamino)-1-propane sulfonates,N-[3-(perfluorooctanesulfonamide)-propyl]-N,N-dimethyl-N-carboxymethyleneammonium betaine, perfluoro alkyl carboxylic acids (e.g. C₇-C₁₃-alkylcarboxylic acids) and salts thereof, perfluorooctane sulfonic aciddiethanolamide, Li, K and Na perfluoro C₄-C₁₂ alkyl sulfonates, Li, Kand Na N-perfluoro C₄-C₁₃ alkane sulfonyl-N-alkyl glycine,fluorosurfactants commercially available under the name Zonyl® (producedby E.I. Du Pont) that have the chemical structure ofRfCH₂CH₂SCH₂CH₂CO₂Li or RfCH₂CH₂O(CH₂CH₂O)_(x) H wherein Rf=F(CF₂CF₂)₃₋₈and x=0 to 25, N-propyl-N-(2-hydroxyethyl)perfluorooctane sulfonamide,2-sulfo-1,4-bis(fluoroalkyl)butanedioate,1,4-bis(fluoroalkyl)-2-[2-N,N,N-trialkylammonium) alkyl amino]butanedioate, perfluoro C₆-C₁₀ alkylsulfonamide propyl sulfonylglycinates,bis-(N-perfluorooctylsulfonyl-N-ethanolaminoethyl)phosphonate,mono-perfluoro C₆-C₁₆ alkyl-ethyl phosphonates, andperfluoroalkylbetaine. Also useful are the fluorocarbon surfactantsdescribed e.g. in U.S. Pat. No. 4,781,985 and in U.S. Pat. No.5,084,340.

Silicon based surfactants are preferably polysiloxanes such aspolysiloxane-polyoxyalkylene copolymers. Such copolymers may be forexample dimethylsiloxane-methyl (polyoxyethylene) copolymer,dimethylsiloxane-methyl (polyoxyethylene-polyoxypropylene) siloxanecopolymer, trisiloxane alkoxylate as a copolymer of trisiloxane andpolyether, and siloxane propoxylate as a copolymer of siloxane andpolypropylene oxide. The siloxane copolymer surfactants may be preparedby any method known to those having skill in the art and can be preparedas random, alternate, block, or graft copolymers. The polyether siloxanecopolymer preferably has a weight-average molecular weight in a range of100 to 10,000. Examples of polyether siloxane copolymers commerciallyavailable in the market include SILWET® DA series, such as SILWET® 408,560 or 806, SILWET® L series such as SILWET-7602® or COATSIL® seriessuch as COATSIL® 1211, manufactured by CK WITCO; KF351A, KF353A, KF354A,KF618, KF945A, KF352A, KF615A, KF6008, KF6001, KF6013, KF6015, KF6016,KF6017, manufactured by SHIN-ETSU; BYK-019, BYK-300, BYK-301, BYK-302,BYK-306, BYK-307, BYK-310, BYK-315, BYK-320, BYK-325, BYK-330, BYK-333,BYK-331, BYK-335, BYK-341, BYK-344, BYK-345, BYK-346, BYK-348,manufactured by BYK-CHEMIE; and GLIDE™ series such as GLIDE™ 450, FLOW™series such as FLOW™ 425, WET™ series such as WET™ 265, manufactured byTEGO.

The permeability to gases is influenced by the swellability of themembrane and by plastization. By plastization compounds penetrate themembrane and act as plasticizer. In humid environments water (vapor) maycause the swelling but also impurities in the gas flow such ashydrocarbon compounds, alcohols, etc. may contribute. Too muchswelling/plastization may reduce the selectivity for polar gases overnon-polar gases and may damage the membrane. The degree of swelling canbe controlled by the types and ratio of monomers, the extent ofcrosslinking (exposure dose, photo-initiator type and amount) and byother ingredients (e.g. chain transfer agents, synergists).

In one embodiment at least two mixtures are coated (simultaneously orconsecutively) on a substrate which after polymerization and dryingresults in a membrane comprising at least one top layer and at least onebottom layer that is closer to the substrate than the top layer. In thisembodiment the top layer comprises the membrane of this invention andthe bottom layer has a porous structure and gives strength to themembrane. For a two-layer membrane structure the bottom layer preferablyhas a dry thickness of between 50 and 500 μm, preferably between 70 and400 μm, most preferably between 100 and 300 μm and the dry thickness ofthe top layer is preferably smaller than 10 μm, preferably between 0.05and 4 μm, most preferably between 0.05 and 1 μm.

Optional additives are polymerizable compounds that comprise one or morefunctional thiol groups. These compounds then act as chain transferagents which are known to be less sensitive to oxygen inhibition andwhose usage result in a more uniform polymer chain length and crosslinkdensity. Examples of thiol compounds include mercaptoacetic acid,mercaptopropionic acid, alkyl mercaptopropionate,mercapto-propylsulfonate, ethyldithiocarbonato-S-sulfopropylester,dimercaptopropane sulfonate mercaptobenzimidazole sulfonate. Preferredthiol compounds are mercaptoethanol, mercaptoethylether,mercaptobenzimidazole, ethyldithioacetate, butanethiol, andethylenedioxydiethanethiol. Optimum quantities depend very much on thecomposition of the crosslinkable composition, on the type of the chaintransfer agent (reactivity) and on the irradiation dose so the optimumconcentration has to be determined case by case. At high levels of chaintransfer agents it was found that adhesion problems may occur if thecompound is in the layer adjacent to the support. When a multilayermembrane is made the chain transfer agent is preferably in the top layerwhere the effect on surface structure is expected to be the highest.Very high levels may retard the crosslinking reaction too much resultingin a layer that is not completely polymerized and is still wet.Preferably the chain transfer agent is present in an amount between0.001 and 1.0 mmol/g polymerizable compound. For most compounds thepreferred range will be between 0.005 and 0.1 mmol/g polymerizablecompound. If the membrane consists of more than one layer the mentionedrange apply to the layer or layers comprising the chain transfer agent.

Other additives may be one or more plasticizers, such as (poly)alkyleneglycol, Glycerol ether and polymer lattices with low Tg-value and thelike and one or more conventional additives, such as acids, pHcontrollers, preservatives, viscosity modifiers c.q. stabilisers,dispersing agents, inhibitors, antifoam agents, organic/inorganic salts,anionic, cationic, non-ionic and/or amphoteric surfactants and the likein accordance with the objects to be achieved.

The above-mentioned additives (photo-initiators, amine synergists,surfactants, chain transfer agents, plasticizers, conventionaladditives) may be selected from those known to a person skilled in theart and may be added in a range of preferably from 0 to 20 weight %based on the composition to be polymerized. Any of the componentsmentioned above may be employed alone or in combination with each other.They may be added after being solubilized in water, dispersed,polymer-dispersed, emulsified or may be converted into oil droplets.

The membrane of the invention may be produced by the following steps:

-   -   Providing a composition comprising a compound comprising at        least 70 oxyethylene groups and at least two polymerizable        groups;    -   Applying the composition to a support;    -   Polymerizing the composition thereby forming a non-porous        polymer film;    -   Optionally washing and/or drying the polymer film.    -   Optionally where the support is non-porous to polar gases        removing the polymerised composition to form an unsupported        membrane.

The polymer film is preferably used as a separation membrane. Thesupport is preferably porous if the polymer film and the support are tobe used in combination.

When high intensity UV light is applied for polymerizing andcrosslinking the crosslinkable composition heat is generated by the UVlamp(s). In many systems cooling by air is applied to prevent the lampsfrom becoming overheated. Still a significant dose of IR light isirradiated together with the UV-beam. In one embodiment the heating-upof the coated support is reduced by placing an IR reflecting quartzplate in between the UV lamp(s) and the coated layer that is guidedunderneath the lamp(s).

As a coating method, any method can be used. For example, curtaincoating, extrusion coating, air-knife coating, slide coating, rollcoating method, reverse roll coating, dip coating, rod bar coating andspray coating. The coating of multiple layers can be done simultaneouslyor consecutively, depending on the embodiments used. In order to producea sufficiently flowable composition for use in a high speed coatingmachine, it is preferred that the viscosity does not exceed 4000 mPa·sat 35° C. (all viscosities mentioned herein are measured at 35° C.,unless indicated otherwise), more preferably that it should not exceed1000 mPa·s at 35° C. For coating methods such as slide bead coating thepreferred viscosity is from 1 to 100 mPa·s. The desired viscosity ispreferably achieved by controlling the amount of solvent, preferablywater.

With suitable coating techniques coating speeds of at least 15 m/min,e.g. more than 20 m/min or even higher, such as 60 m/min, 120 m/min ormore, up to 400 m/min, can be reached. To reach the desired dose at highcoating speeds more than one UV lamp may be required, so that the coatedlayer is exposed to more than one lamp. When two or more lamps areapplied all lamps may give an equal dose or each lamp may have anindividual setting. For instance the first lamp may give a higher dosethan the second and following lamps or the exposure intensity of thefirst lamp may be lower.

Before applying the coating to the surface of the support materialdescribed above this support may be subjected to a corona dischargetreatment, glow discharge treatment, flame treatment, ultraviolet lightirradiation treatment and the like, for the purpose of improving thewettability and the adhesiveness.

Whereas it is possible to practice the invention on a batch basis with astationary support surface, to gain full advantage of the invention, itis much preferred to practice it on a continuous basis using a movingsupport surface such as a roll-driven continuous web or belt. Using suchapparatus the polymerizable composition can be made on a continuousbasis or it can be made on a large batch basis, and the compositionapplied continuously onto the upstream end of the driven continuous beltsupport surface, the polymerization effecting means (such as anirradiation source, a heat source, a plasma generator) being locatedabove the belt downstream of the composition application station and themembrane removal station—if applicable—being further downstream of thebelt, the membrane being removed in the form of a continuous sheetthereof. Removal of any water or solvent from the membrane can beaccomplished either before or after the membrane is taken from the belt.For this embodiment and all others where it is desired to remove themembrane from the support surface, it is, of course, preferable that thesupport surface be such as to facilitate as much as possible the removalof the membrane therefrom. Typical of the support surfaces useful forthe practice of such embodiments have a low surface energy and aresmooth, stainless steel sheet or, better yet, teflon or teflon-coatedmetal sheet. Rather than using a continuous belt, the support surfacecan be of an expendable material, such as release paper, resin coatedpaper, plastic film, or the like (but not soluble in the solvent whenpresent), in the form of a roll thereof such that it can be continuouslyunrolled from the roll, upstream of the solution application station, asa continuous driven length and then rerolled, with the membrane thereon,downstream of the radiation station. In another embodiment the membraneis not separated from the support in which case the support ispreferably sufficiently porous to enable a high flux through themembrane. Examples of porous support include woven materials, non-wovenmaterials, porous polymeric membranes, porous inorganic membranes. Theporous support is not limited to sheet form, also porous supports intubular form like hollow fibers can be used. Removal of the solventpreferably is done before rerolling the support with the membranethereon but may also be done at a later stage.

The membrane of the invention is preferably used in a module wherein themembrane is assembled into a cartridge. The membrane geometry influencesthe manner in which the membrane is packaged. The preferred membranecartridge geometries are flatsheet, spiral-wound and hollow-fiber.

While we have emphasised the usefulness of the membranes of the presentinvention for separating gases it will be understood that the presentinvention is not limited to gas permeable membranes.

The present invention will be illustrated in more detail by thefollowing non-limiting examples. Unless stated otherwise, all givenratios and amounts are based on weight.

EXAMPLES

Preparation of the Membrane

A mixture was prepared for each example as described below.

The mixture was coated on a glass plate by a bar coater (Spiral wound KBar from R K Print Coat Instruments Ltd.) at 200 micrometer coatingthickness, and cured three times by exposure to UV light using aLight-Hammer™ fitted in a bench-top conveyor LC6E (both supplied byFusion UV Systems) with 100% UV power (D-bulb) and a conveyer speed of 5m/min.The cured film (membrane) was removed from the glass plate and dried at40° C. for 30 min.Evaluation of the Physical Property of the MembraneThe physical strength (bendability) of the membrane was evaluated bybending the obtained free film around a plastic plate of 3 mm thicknessand ranked A-E according the result of the test.

-   A: 180° bendable without breaking,-   B: breaks between 120° and 180°,-   C: breaks between 90° and 120°,-   D: breaks between 60° and 90°,-   E: breaks at <60°    Calculation of EO Content of the Membrane

The EO content of the membrane is calculated by determining the EOcontent of the non volatile components whereby the support is notincluded—in case the membrane is not separated from the support. The EOcontent is calculated as follows: EO content={(wt % of each non-volatilecompound)*(avg MW of oxyethylene fraction in each non-volatilecompound)/(avg. MW of each non-volatile compound)}/{total solidcontent}, wherein the total solid content of the composition is foiniedby the non-volatile components.

Evaluation of the Gas Permeability

Flux of CO₂ and N₂ through the obtained film was measured at 80° C. andgas feed pressure of 2000 kPa (20 bar) using a gas permeation cell fromMillipore with a measurement diameter of 4.2 cm for each gas separately.Permeability P was calculated based on the following equation.P=F×L×10⁻¹²/(60×A×p)(unit: m³(STP)·m/m^(2·s·KPa))Where F is gas flow (SCCM), L is membrane thickness (micrometer), A ismembrane area=0.001385 m², p is feed gas pressure (kPa), and “×” standsfor multiply. STP is Standard Temperature and Pressure, which is 0° C.and 1 atm, thus 1 m³ (STP) is 1 m³ at STP condition, SCCM is “standardcc/min”, which is flow (cc/min) at STP condition (cm³(STP)/min=×10⁻⁶m³(STP)/min). Gas flow is measured by a digital flow meter. Selectivity(_(CO2/N2)) was calculated based on following equation._(CO2/N2) =P _(CO2) /P _(N2)

Comparative Example 1

50 parts of PEG600DA (Poly(ethylene glycol) diacrylate, average Mn=700from Sigma Aldrich) were mixed with 0.09 parts of Zonyl™ FSN 100 (fromDuPont), 0.5 parts of Additol™ HDMAP(2-hydroxy-2-methyl-1-phenyl-1-propanone from Cytec SurfaceSpecialities), and 49.4 parts of water.

-   The mixture was coated and cured according the procedure mentioned    above, and evaluated.-   The cured mixture before drying had a gel-like appearance and after    drying the film could be removed from the glass plate but was very    easy to break (not bendable).-   Thickness of the dried film was 150 micron.-   The CO₂ flow through the film was 1.58 SCCM, and the N₂ flow was    below detection limit of the flow meter (0.2 SCCM). Therefore the    CO₂ permeability is: (1.58×150×10⁻¹²)/(60×0.001385×2000)=1.426×10⁻¹²    m³(STP)·m/m²·s·kPa.-   Since the N₂ flow is less than 0.2 SCCM, the N₂ permeability is less    than 0.18 m³(STP)·m/m²·s·kPa (=(0.2×150×10⁻¹²)/(60×0.001385×2000)),    therefore the CO₂/N₂ selectivity _(CO2/N2)=P_(CO2)/P_(N2) is more    than 1.426/0.18=7.9.-   Oxyethylene (EO) content of PEG600DA is 82.0%, the EO content of    Zonyl™ FSN100 was estimated as 60%. Additol™ HDMAP does not contain    EO-groups. The EO content of the polymer film was therefore 81.2%.

Comparative Example 2

Comparative Example 2 was done according the same procedure as inComparative Example 1, except that PEG2000DA (Poly(ethylene glycol) 2000diacrylate (Mn=2126) from Monomer-Polymer & Dajac Laboratories, Inc.)was used instead of PEG600DA. The result is shown in Table 1.Oxyethylene (EO) content of PEG2000DA is 94.1%; the EO content of thepolymer film was therefore 93.1%.

Example 1

Examples 1 was done according the same procedure as in ComparativeExample 1, except that PEG4000DA (Poly(ethylene glycol) 4000 diacrylate(Mn=4126) from Monomer-Polymer & Dajac Laboratories, Inc.) was usedinstead of CD9038. The result is shown in Table 1.Oxyethylene (EO) content of PEG4000DA is 96.9%, the EO content of thepolymer film was therefore 95.9%.

Example 2

Examples 1 was done according the same procedure as in ComparativeExample 1, except that PEG4000DMA (Poly(ethylene glycol) 4000dimethacrylate (Mn=4154) from Monomer-Polymer & Dajac Laboratories,Inc.) was used instead of PEG600DA. The result is shown in Table 1.Oxyethylene (EO) content of PEG4000DMA is 96.3%, the EO content of thepolymer film was therefore 95.3%.

Comparative Example 3

Comparative Example 3 was done according the same procedure as inExample 1, except that 25 parts of PEG600DA and 25 parts MPEG-A(Poly(ethylene glycol) methyl ether acrylate Mn˜454, from Sigma Aldrich)were used instead of 50 parts of PEG600DA. The result is shown in Table1.Oxyethylene (EO) content of MPEG-A is 81.1%, the EO content of thepolymer film was therefore 80.7%.

Example 3

Examples 3 was done according the same procedure as in ComparativeExample 3, except that PEG4000DA (Poly(ethylene glycol) 4000 diacrylate(Mn=4126) from Monomer-Polymer & Dajac Laboratories, Inc.) was usedinstead of PEG600DA. The result is shown in Table 1.The EO content of the polymer film was 88.1%.

TABLE 1 Bend monomer vinyl group N Mn ability CO₂ permeability P CO2/N2Comparative PEG 600DA acrylate 13 742 E 1.425 >8 Example 1 ComparativePEG 2000DA acrylate 45 2126 B 3.65 >20 Example 2 Example 1 PEG 4000DAacrylate 91 4126 A 4.70 >26 Example 2 PEG 4000DMA methacrylate 91 4154 A4.52 >25 Comparative PEG 600DA/ acrylate 13 742 D 3.05 >17 Example 3MPEGA Example 3 PEG 4000DA/ acrylate 91 4126 A 6.11 >34 MPEGA f:functionality of the cross-linkable monomer (number of unsaturatedgroups in the cross-linkable monomer) n: number of oxyethylene groups(CH₂CH₂O) in the cross-linkable monomer. Mn: molecular weight of thecross-linkable monomer. Unit of permeability P: ×10⁻¹² m³(STP) · m/m² ·s · kPaThe water permeance at 20° C. of the membranes was found be lower than1.4×10⁻⁹ m³/m²·s·kPa.Results

-   The polymerization of all examples by curing with UV light went OK.-   Observation of the membrane surface and cross section by SEM    (scanning electron microscope) showed that no pores were visible    indicating that the pore sizes—if present—are smaller than 10 nm.-   The physical strength (bendability) of the membrane was best with    the polymerizable compound having the largest number of oxyethylene    units.-   Using polymerizable compounds with a large number of oxyethylene    units resulted in high permeability values.-   The results obtained with mixtures of polymerizable compounds and    monofunctional monomers are in agreement with the results with    polymerizable compounds only except that with the mixtures higher    permeability values are obtained. This result can be explained by a    lower cross-linking density because the monofunctional monomers are    cured into the matrix but do not contribute to the crosslinking    density. In these experiments the best result is obtained with the    combination of compounds with a high number of oxyethylene    units (91) and monofunctional monomers.-   Due to the very low nitrogen flow below the detection limit of the    flow meter used (down to 0.2 SCCM), only a minimum value for the    selectivity could be confirmed.

1. Membrane comprising a continuous substantially non-porous layercomprising the polymerization product of a compound, which compoundcomprises at least 70 oxyethylene groups forming an uninterrupted chainof the formula —(CH₂CH₂O)_(n)—wherein n is at least 70 and at least twopolymerizable groups, wherein the pure water permeance of the membraneat 20° C. is less than 6.10⁻⁸ m³/m²s kPa.
 2. Membrane according to claim1 wherein said polymerizable groups are selected from acrylate groups,methacrylate groups, acrylamide groups, vinyl ether groups, vinyl estergroups, vinyl amide groups, allyl ether groups, allyl ester groups,allyl amine groups, allyl amide groups, styryl groups and combinationsthereof.
 3. Membrane according to claim 1 wherein at least one of saidpolymerizable groups is an acrylate group or a methacrylate group. 4.Membrane according to claim 1 wherein said compound constitutes 3-80weight % of the composition to be polymerized.
 5. Membrane according toclaim 1 wherein said continuous substantially non-porous layer comprisesat least 60 weight % of oxyethylene groups.
 6. Membrane according toclaim 1 wherein said continuous substantially non-porous layer comprisesat least 90 weight % of oxyethylene groups.
 7. Membrane according toclaim 1 wherein said compound comprises poly(ethylene glycol) 4000diacrylate.
 8. Membrane according to claim 1 having a dry thickness ofbetween 0.05 and 10 μm.
 9. Membrane according to claim 1 for separatinggases.
 10. Membrane according to claim 3 wherein said continuoussubstantially non-porous layer comprises at least 90 weight % ofoxyethylene groups.
 11. Membrane according to claim 4 wherein saidcontinuous substantially non-porous layer comprises at least 90 weight %of oxyethylene groups.
 12. Membrane according to claim 1 for separatinggases wherein said continuous substantially non-porous layer comprisesat least 90 weight % of oxyethylene groups, at least one of saidpolymerizable groups is an acrylate group or a methacrylate group andthe membrane has a dry thickness of between 0.05 and 10 μm.
 13. A modulecomprising at least one cartridge and at least one membrane according toclaim
 1. 14. A module comprising at least one cartridge and at least onemembrane according to claim
 12. 15. Process for making a membraneaccording to claim 1 comprising the steps of: a. providing a compositioncomprising a compound comprising at least 70 oxyethylene groups and atleast two polymerizable groups; b. applying said composition to asupport; c. polymerizing said composition thereby forming asubstantially non-porous polymer film; d. optionally separating thepolymer film from the support; e. optionally washing and/or drying thepolymer film.
 16. Process according to claim 15 wherein the coating stepis continuous and wherein the polymerization step comprises exposure ofthe applied layer to radiation.
 17. Process according to claim 16wherein the exposure is for less than 1 second.
 18. Process according toclaim 15 wherein the membrane has a dry thickness of between 0.05 and 10μm.
 19. Process according to claim 17 wherein the membrane has a drythickness of between 0.05 and 10 μm.
 20. Process according to claim 15wherein the coating step is continuous, the polymerization stepcomprises exposure of the applied layer to radiation for less than 1second, the membrane has a dry thickness of between 0.05 and 10 μm andthe composition is applied to the support at a coating speed of at least15m/min.